Method of an apparatus for the automatic supervision of liquid limits in closed tanks

ABSTRACT

A level detector for a tank for liquid comprises a dip tube having an open lower end within the tank. At its upper end the tube carries a pressure detector and a restricted orifice communicates the tube with an environment external to the tank. A higher gas pressure is produced in the tank than in said environment e.g. by the introduction of liquid into the tank and the pressure within the dip tube remains substantially the same as that in the tank until the lower end of the dip tube is immersed, causing a drop in pressure within the dip tube. This drop in pressure is used to control the introduction or removal of liquid from the tank to limit the level to a desired value. In a variant two dip tubes are used for each level each having its own restricted orifice communicating with said environment and one having its lower end slightly below the other, and the pressure detection means is responsive to the differential pressure between the dip tubes.

United States Patent Ralet et a1.

Clement Ralet, both of 661 Boulevard Poincare, Brussels, Belgium [22]Filed: June 25,1970

[21] Appl.No.: 49,719

[30] Foreign Application Priority Data June 26, 1969 Belgium ..735,l69

s2 U.S.Cl ..l37/206,l37/386,73/298 s1 lnt.Cl. ..c01r23/14 5sFieldofSearch.. ....l37/403,393,154,206,386;

[5 6] References Cited UNITED STATES PATENTS 1,020,642 3/1912 Elkofer..137/393 Trethewey ...137/403 X Mylander 137/393 Primary ExaminerAlanCohan Attorney-John Lezdey [57] ABSTRACT A level detector for a tank forliquid comprises a dip tube having an open lower end within the tank. Atits upper end the tube carries a pressure detector and a restrictedorifice communicates the tube with an environment external to the tank.A higher gas pressure is produced in the tank than in said environmente.g. by the introduction of liquid into the tank and the pressure withinthe dip tube remains substantially the same as that in the tank untilthe lower end of the dip tube is immersed, causing a drop in pressurewithin the dip tube. This drop in pressure is used to control theintroduction or removal of liquid from the tank to limit the level to adesired value. In a variant two dip tubes are used for each level eachhaving its own restricted orifice communicating with said environmentand one having its lower end slightly below the other, and the pressuredetection means is responsive to the differential pressure between thedip tubes.

15 Claims, 4 Drawing Figures 'PATENTEDMAYEB I972 3,664,865

manor. mam tamesr vamaum mm mm RJHNVENTOR BY Q-n m ATTORNEY g i i METHODOF AN APPARATUS FOR THE AUTOMATIC SUPERVISION OF LIQUID LIMITS IN CLOSEDTANKS This invention relates to closed pressurized or unpressurizedtanks in which automatic level control based on control of the supplyand removal of liquid is required, for example where it is desired toprovide top-level stopping and bottom-level starting of a pump supplyinga water supply air tank i.e. apressurized tank associated with an aircompressor, or where, in pressurized vented tanks, such as fuel oiltanks, it is necessary to prevent accidental spillage during refuellingby ensuring that the filling facility stops automatically when thedesired upper liquid level is reached.

It is an object of the invention to provide a method and a paratus forthe automatic supervision of limits of liquid level in closed tanks.

The invention provides detection of the critical levels by means of acritical pressure acting an extensible member as a result of the abruptsubstitution of a dynamic condition for a static equilibrium.

Several ways are known of using a critical pressure in association withan extensible member to supervise critical levels. For instance, it isknown for diaphragm-fitted domes to be placed at the bottom of a tank,the domes distorting more in proportion as the liquid level rises. Alsoknown are air bubbling facilities in which a diaphragm reflects thepressure required for bubbles to pass. French Pat. No. 1,548,929discloses a diaphragm detector which is disposed at the top of a diptube and which operates, once the liquid has reached the dip tube end,in accordance with the compression of the air trapped in the dip tube.

The invention, however, is based on novel features enabling a clear andinstantaneous pressure signal to be produced by. a small variation inliquid level, the clearness of the pressure signal being the result ofthe abrupt changeover from a moving-gas condition to a staticequilibrium position.

These features will be studied hereinafter in greater detail and ananalysis will be given of how the physical principles are used. Thepressure-sensitive members are connected to air or gas circuits suppliedthrough dip tubes which extend through the tank top wall down to thelevels to be supervised. These circuits have a small orifice to providea leak which discharges to a lower-pressure environment. When the end ofa dip tube is above the liquid, there is a small leakage rate of flow tothe lower-pressure environment. Since the cross-section of the leakorifice is small, the resulting pressure loss is equivalent to thedifference between the pressure, with the result that the higher gaspressure i.e. the gas pressure above the liquid is also the gas pressurein the corresponding detector chamber.

Considering now the brief critical time when the rising liquid almosttouches the dip tube end, the constriction of the passage between thesurface of the liquid and the tube end starts to reduce the gas flow;since the interior of the tube and thus the leak orifice ceases to besupplied freely, the pressure in the sensitive member starts to drop.This time is short, for the liquid, once it has touched the bottom ofthe tube, rises therein to a level corresponding to the pressuredifference, the leak providing communication with the low-pressureenvironment. The detector must be connected at a height placing it outof reach of the liquid column. Thus there is an abrupt change from thecondition in which the gas is moving freely up the tube to the conditionin which static equilibrium exists with a column of liquid in the tube,the extensible member simultaneously changing over abruptly from thehigh pressure condition to the lower pressure condition.

As an advantageous way of appreciably improving the operation of theinvention, a pressure regulator is placed in a line connecting the tankto the lower-pressure environment for example in the vent pipe in thevery common case of storage tanks such as fuel oil tanks, for aspreviously explained, the pressure-sensitive member must be placed highenough not to be reached by a liquid column equal to the pressuredifference between the air cushion in the tank and the low-pressureenvironment and thus the pressure in the tank must not be allowed toreach too high a value. The maximum value of this pressure differencemust therefore be limited. Also, if the pressure detectors are tooperate satisfactorily and to be satisfactorily sensitive, the pressuredifierence must remain within appropriate limits. It is thereforedesirable to provide regulation of the pressure difference. Theregulator can be embodied quite simply in the form of a calibrated valvecomprising a weight capsule which is lifted a varying distance from itsseat by the air flow. An increased rate of air flow lifts the capsulehigher and vice-versa, capsule weight forming the pressure differenceset-value.

The continuous air or gas consumption which is either necessary tosupply the leaks according to the invention or desirable for thepurposes of regulation as just described is not necessarily adisadvantage, for in the frequent cases in which tanks are connected toatmosphere by a vent pipe, an air source which can be used for ananti-spill system according to the invention is available quitenaturally during filling since the entering liquid expels an equivalentvolume of air, and the positive pressure of the air cushion is equal tothe pressure loss of the air passing through the vent pipe. In tanks ofthis kind, the small leaks associated with the dip tubes go toatmosphere.

The invention operates very satisfactorily with an aircushion positivepressure of the order of 60 mm water column. Conveniently, the vent isgenerously dimensioned and receives a valve calibrated by a weightcorresponding to this required pressure.

In the method according to the invention, at least onepressure-sensitive member is associated with at least one clip tubeextending into the tank and having its lower end within the tank open,said dip tube enabling a small level variation in the tank to cause adynamic gas flow state (in which gas flows freely up the dip tube) to bereplaced by a static equilibrium condition (in which the lower end ofthe dip tube is closed by a liquid column) or vice-versa. A leak orificeis provided from the or each dip tube arranged to produce a pressureloss so that the tube top part may communicate with an environment at alower pressure, and the sensitive member, which is disposed at a heightabove the lower end of the dip tube which is greater than the height ofthe liquid column which would be supported by the pressure differencebetween the interior of the tank and said environment, controls theenergization of a level-determining facility.

Various embodiments of the invention will now be described withreference to the accompany drawings, in

which:

FIG. 1 is a schematic view of a first embodiment;

FIG. 2 is a schematic view of a second embodiment;

' FIG. 3 is a schematic view of a third embodiment; and

FIG. 4 is a schematic view of a fourth embodiment.

Referring to FIG. 1 a closed tank has an air vent 4 with a pressureregulating valve 5 and a filling tube extending to adjacent the bottomof the tank interior, for the introduction of liquid. Extending throughthe top wall of the tank are dip tubes 1 and 2 having open lower ends atslightly different levels within the tank. Pressure detection meanscomprise expansible bellows members P and P mounted on top of the tubes1 and 2 and providing compartments communicating with the interior ofthe respective dip tubes. Leak orifices F and F are provided in thebellows members P and P respectively communicating the interior of diptubes 1 and 2 respectively with atmosphere.

A tilting mercury switch having a bulb 3 is carried on a beam extendingacross the tops of the bellows members.

In operation, with the tank substantially empty, the operator presses astart button and filling begins. The two bellows inflate at the samerate, the beam and the bulb 3 remaining horizontal and the mercury beadproviding a current path for the control circuit. When the liquidreaches the level of the bottom of tube 1, bellows P discharges throughleak orifice F,, the bulb 3 tilts and contact is interrupted, so thatfilling stops automatically. The use of a differential detector has theadvantage that the initial phase of filling can then proceed without theneed for any further facilities, for if a single set of bellows, likethe bellows P of FIG. 2, is used, contact cannot be made until the airpressure within the tank has built up, and so unless some specialfacility is provided the installation cannot be started. Such facilitytakes the form of a delay facility having a temporary contact whichshunts the contact of the missing detector for the few seconds requiredto produce air cushion pressure.

FIG. 2 shows how the delay facility can be embodied electrically, in anarrangement in which expanded one clip tube 3 and one bellows P is used,the bellows P in its expanded position closing a switch 13 to provide acurrent path to the control circuit. In the arrangement of FIG. 2 thereis the advantage that there is a positive safety feature in that anyelectrical fault stops filling. To make up for the initial opening ofthe contact 13, before the bellows P has expanded, a switch 16 of adelayed-break dashpot relay 6 is placed in parallel with switch 13.Prior to filling the facility has been set or cocked by a button switch7 which energizes the system and causes switch 16 to close as a resultof winding S6 of the relay being energized by the current flowing afterthe closure of switch 7. Starting proper is initiated by operation of abutton 8 which acts simultaneously on a normally closed switch NF6 andon a normally open switch N09, the opening of the normally closed switchNF6 de-energizing winding S6 by interrupting the current flowingtherethrough, the armature rising slowly with retardation by dashpot D6.The normally open switch N09 causes opening of an electromagneticallyoperable valve S9 which controls filling of the tank. At the end of thedashpot delay, switch 16 is again opened, by which time air pressure hasbuilt up in the tank and thereafter the valve S9 is under the control ofthe detector P which stays inflated only until the liquid level reachesthe bottom of dip tube 3. Thereafter bellows P deflates through the leakorifice F and the switch 13 is opened, causing the valve S9 to close.

Electronic or pneumatic control systems can be used advantageously inthe present context, in place of the electromechanical system shown.

Nor will the scope of the invention be exceeded if a brief manualoperation is used to make up for the initial open condition of theswitch 13 due to the lack of a positive pressure in the tank whenfilling begins. The invention can therefore be applied to a pouringpistol having a trigger-retaining device which is rigidly secured to theextensible member (e.g. a bellows such as P This device would bearranged to operate immediately the air cushion has formed and to becomeinoperative upon de-flation of the bellows immediately the liquidreaches the stop level, so that the pistol closes automatically.

' The practical advantage of the single-chamber detector of FIG. 2, withor without a delay facility, is that the detector and associated devicescan be installed on a tanker vehicle and the driver has to connect uponly a single detection hose (to the tube 3) before discharging fuelinto the tank.

The embodiment shown in FIG. 3 combines the advantage of obviating thedelay feature with the advantage of there being only a single hose toconnect between the tanker and the tank to be filled therefrom. Thepressure detector in FIG. 3 is embodied by a container comprising twodomes or chambers 11, 12 separated by a prestretched rubber diaphragm.Dome 11 is connected with a dip tube 1, extending to the stop level, andwith a leak orifice F whereas dome 12 is connected to a dip tube 2,extending into the tank but stopping higher than hose 1, and with a leakorifice F When the two pressures are in the chambers 11 and 12 areequal, the diaphragm, as a result of its stretched state, closes a valveseat at the end of a conduit 9 which extends into the chamber 12. Whenthe liquid reaches the bottom of the tube 1, the pressure in dome 11 isthereby reduced, and the pressure differential between the domes 11 and12 moves the diaphragm away from the end of conduit 9. Communicationbetween the interior of the tank and the conduit 9 therefore occurs inthe dome 12. Conduit 9 which may be a hose for most of its length, isconnected to a second bellows type pressure detector P9 which acts on anormally closed electrical or pneumatic switch, for in this embodimentthe reaching of the stop level corresponds to inflation of bellows P9,whereas in the embodiment of FIG. 2 the bellows P deflated when theliquid reached the stop level.

Referring to FIG. 4, consideration will now be given to how theinvention can be used in a pressure tank 41 continuously supplied withair by a compressor 42. The tank is required to be supplied with waterintermittently by a pump 43 which starts when the water falls to a lowerlevel and stops when the water rises to an upper level. Also, the waterdistribution from the tank 41 through line 44 is required to be at avery constant pressure. It will be assumed that tank 41 has beeninstalled in a cellar and communicates via a riser 45 with a bufferreservoir 46 in an attic. Air can escape from reservoir 46 via acalibrated valve 48 serving as pressure regulator. The weight of valve48 is adjusted so that the air pressure in attic reservoir 46 is e.g. 5kglcm A calibrated valve 47 in riser 45 serves as air pressuredifference regulator. It will be assumed that the air pressuredifference between the upper and lower tanks 46 and 47 is e.g. 0.5kg/cm, so that the air in the tank 41 is at a pressure of 5.5 kglcm Inaddition to the riser 45, two pairs of tubes 1-4 of much narrowercross-section than the riser 45 interconnect the two tanks 41 and 46.Four restricted throttle orifices F F F F serving to produce the leaksrequired for the purposes of this invention are disposed at the placeswhere the four narrow tubes 14 enter the attic tank 46, and adifferential pressure sensing device such as that enclosed in the domes11 and 12 in FIG. 3 is connected between the tubes. 1 and 2, and anotherbetween the tubes 3 and 4, said devices being referenced 10 and 20respectively.

If the water reaches none of the dip tubes, the leakage rate of flow issuch that the pressure loss is 0.5 kg/cm and the device 10 operates tostart the pump 43. If the water reaches the bottom of any dip tube, itrises 5 meters therein and the leak therethrough ceases. The pressuredifference detectors 10, 20 are connected to the system at a height ofat least 5 meters above the cellar. One pair of dip tubes per level isprovided, and the immersed lengths of each pair are similar. Thus, tubes1 and 2 are for the lower level and tubes 3 and 4 are for the upperlevel. The tubes of each pair have their lower ends at slightlydifferent levels.

The detector produces a brief signal for the time taken by the waterlevel to travel the difference between the lengths of the tubes of anysingle pair. In the case of the pair supervising the bottom level, thissignal acts on the pump contactor start button, and the signal output bythe top level pair acts on the stop button.

The invention is therefore of use in a wide variety of circumstances.Other possible examples are controlling the bottom level of a tank fromwhich liquid is being discharges by compressed air. Operation is thesame as at the bottom level of the cellar tank just described i.e. theliquid column is in static equilibrium in the detecting tubes until thetube bottom emerges from the liquid, thus indicating that the tube hasemptied so that there is an air flow in the leak.

We claim:

1. Apparatus comprising a closed tank, means for providing a higher gaspressure within said tank than in an environment outside the tank, a diptube extending into said tank and having an open lower end within saidtank, a restricted orifice communicating said clip tube with saidenvironment, means for controlling the passage of liquid into or out ofsaid tank, pressure detecting means for detecting the gas pressurewithin said clip tube, said pressure detecting means controlling saidliquid passage controlling means in accordance with the gas pressurewithin said clip tube.

2. The apparatus of claim 1 comprising a further dip tube extending intosaid tank and having an open lower end within said tank at a levelslightly different from said open lower end of the first mentioned saiddip tube a restricted orifice connecting said further dip tube with saidenvironment, said pressure detecting means being operable in accordancewith the pressure difference between said dip tubes.

3. The apparatus of claim 1 wherein said means for providing said higherpressure within said tank includes a restricted vent from said tank tosaid environment.

4. The apparatus of claim 3 wherein a pressure regulating valve isdisposed in said vent.

5. The apparatus of claim 3 wherein said pressure detecting means isarranged to allow passage of liquid into said tank by said liquidpassage controlling means if the pressure within said dip tube is abovethe pressure of said environment and wherein means is provided tocountermand said pressure detecting means at the start of theintroduction of liquid into said tank, until said higher pressure hasbeen reached.

6. The apparatus of claim 2 wherein said pressure detecting meanscomprises a chamber divided into two compartments by a resilientdiaphragm, each said chamber being connected to a different one of saidtubes, a conduit extending into one of said chambers and terminating ina seal arranged to be closed by said diaphragm in the position of thelatter adopted when the pressure in each of said chambers is equal, afurther restricted orifice connecting said conduit with said environmentand a pressure detecting device communicating with said conduit, forproducing a signal upon a change in the gas pressure in said conduit.

7. The apparatus of claim 2 wherein said means for producing said higherpressure in the tank comprises an air compressor discharging into saidtank, and wherein said environment is provided by a further tank at ahigher level than the first mentioned tank, one such pair of dip tubesbeing provided to define an upper level limit and a lower level limit, aconduit connecting said tanks, and throttling means in said conduit,each said pair of dip tubes having a separate pressure detection meansfor detecting a pressure difference between the tubes of the pair,

8. In an apparatus for the automatic supervision of limits of liquidlevels in closed tanks, in which a pressure variation acting on anextensible member is used to detect the liquid level, and in which atleast one pressure-sensitive member is associated with means enabling asmall level variation to cause a dynamic gas flow state to be replacedby a state of static pressure equilibrium or vice-versa, wherein saidmeans comprises an air circuit having at least one tube whose bottompart extends through the tank top wall and dips down as far as thesupervised liquid level, the upper part of said tube top partcommunicating via a restriction with an environment at a lower pressurethan the interior of the tank, and said pressure sensitive member beingconnected to said tube at a level above the level of the liquid columnin said tube measuring the pressure difference between the interior ofthe tank and said environ ment and controlling the energization of alevel-determining facility.

9. The apparatus according to claim 8 which includes a pressuredifference regulator disposed in a line connecting the tank to thelower-pressure environment.

10. The apparatus according to claim 9 wherein the pressure differenceregulator is a calibrated valve whose weight is adjusted to the requiredpressure difference.

11. The apparatus according to claim 8 wherein said dip tubecommunicates with the atmosphere and the rate of air flow and the airpressure supplying said circuit depending on the compression of the airin said tank by make-up liquid and upon the resistance of a vent to theremoval of such air from said tank.

12. The apparatus according to claim 9, wherein said pressure differenceregulator has one side connected to a leakage circuit comprising a diptube communicating with the supervised liquid level and the other sideconnected to a leakage circuit having a dip tube communicating with alevel higher than the supervised level, whereby the difference betweenthe pressure causes filling to cause when the end of the longer tubebecomes immersed.

13. The apparatus according to claim 8, in which a single leakagecircuit is associated with a single extensible nondifferential memberand which includes delay means to com ensate for the absence of fillingauthorization signal resu ting from the lack of air pressure at thebeginning of filling.

14. The apparatus according to claim 9, in which said pressuredifference regulator has two compartments separated by a prestressedresilient diaphragm whereby in the event of a pressure difference theentry of a tube connecting the air circuit communicating with the topintake to a third small-leak circuit is opened, said third small-leakcircuit comprising an extensible member which upon pressurizationproduces a toplevel signal.

15. A system comprising the apparatus of claim 8 in association with awater supply air tank supplied continuously by an air compressor whereinthe higher-pressure environment takes the form of a tank at a higherlevel than the water supply air tank and in which the leakages from twopairs of detection dip pipes of similar but unequal lengths enter thehigher-level tank, one pair of dip pipes indicating the top level andthe other pair indicating the bottom level, and the pipes of these pairscommunicating with pressure difference regulators.

1. Apparatus comprising a closed tank, means for providing a higher gaspressure within said tank than in an environment outside the tank, a diptube extending into said tank and having an open lower end within saidtank, a restricted orifice communicating said dip tube with saidenvironment, means for controlling the passage of liquid into or out ofsaid tank, pressure detecting means for detecting the gas pressurewithin said dip tube, said pressure detecting means controlling saidliquid passage controlling means in accordance with the gas pressurewithin said dip tube.
 2. The apparatus of claim 1 comprising a furtherdip tube extending into said tank and having an open lower end withinsaid tank at a level slightly different from said open lower end of thefirst mentioned said dip tube a restricted orifice connecting saidfurther dip tube with said environment, said pressure detecting meansbeing operable in accordance with the pressure difference between saiddip tubes.
 3. The apparatus of claim 1 wherein said means for providingsaid higher pressure within said tank includes a restricted vent fromsaid tank to said environment.
 4. The apparatus of claim 3 wherein apressure regulating valve is disposed in said vent.
 5. The apparatus ofclaim 3 wherein said pressure detecting means is arranged to allowpassage of liquid into said tank by said liquid passage controllingmeans if the pressure within said dip tube is above the pressure of saidenvironment and wherein means is provided to countermand said pressuredetecting means at the start of the introduction of liquid into saidtank, until said higher pressure has been reached.
 6. The apparatus ofclaim 2 wherein said pressure detecting means comprises a chamberdivided into two compartments by a resilient diaphragm, each saidchamber being connected to a different one of said tubes, a conduitextending into one of said chambers and terminating in a seal arrAngedto be closed by said diaphragm in the position of the latter adoptedwhen the pressure in each of said chambers is equal, a furtherrestricted orifice connecting said conduit with said environment and apressure detecting device communicating with said conduit, for producinga signal upon a change in the gas pressure in said conduit.
 7. Theapparatus of claim 2 wherein said means for producing said higherpressure in the tank comprises an air compressor discharging into saidtank, and wherein said environment is provided by a further tank at ahigher level than the first mentioned tank, one such pair of dip tubesbeing provided to define an upper level limit and a lower level limit, aconduit connecting said tanks, and throttling means in said conduit,each said pair of dip tubes having a separate pressure detection meansfor detecting a pressure difference between the tubes of the pair.
 8. Inan apparatus for the automatic supervision of limits of liquid levels inclosed tanks, in which a pressure variation acting on an extensiblemember is used to detect the liquid level, and in which at least onepressure-sensitive member is associated with means enabling a smalllevel variation to cause a dynamic gas flow state to be replaced by astate of static pressure equilibrium or vice-versa, wherein said meanscomprises an air circuit having at least one tube whose bottom partextends through the tank top wall and dips down as far as the supervisedliquid level, the upper part of said tube top part communicating via arestriction with an environment at a lower pressure than the interior ofthe tank, and said pressure sensitive member being connected to saidtube at a level above the level of the liquid column in said tubemeasuring the pressure difference between the interior of the tank andsaid environment and controlling the energization of a level-determiningfacility.
 9. The apparatus according to claim 8 which includes apressure difference regulator disposed in a line connecting the tank tothe lower-pressure environment.
 10. The apparatus according to claim 9wherein the pressure difference regulator is a calibrated valve whoseweight is adjusted to the required pressure difference.
 11. Theapparatus according to claim 8 wherein said dip tube communicates withthe atmosphere and the rate of air flow and the air pressure supplyingsaid circuit depending on the compression of the air in said tank bymake-up liquid and upon the resistance of a vent to the removal of suchair from said tank.
 12. The apparatus according to claim 9, wherein saidpressure difference regulator has one side connected to a leakagecircuit comprising a dip tube communicating with the supervised liquidlevel and the other side connected to a leakage circuit having a diptube communicating with a level higher than the supervised level,whereby the difference between the pressure causes filling to cause whenthe end of the longer tube becomes immersed.
 13. The apparatus accordingto claim 8, in which a single leakage circuit is associated with asingle extensible nondifferential member and which includes delay meansto compensate for the absence of filling authorization signal resultingfrom the lack of air pressure at the beginning of filling.
 14. Theapparatus according to claim 9, in which said pressure differenceregulator has two compartments separated by a prestressed resilientdiaphragm whereby in the event of a pressure difference the entry of atube connecting the air circuit communicating with the top intake to athird small-leak circuit is opened, said third small-leak circuitcomprising an extensible member which upon pressurization produces atop-level signal.
 15. A system comprising the apparatus of claim 8 inassociation with a water supply air tank supplied continuously by an aircompressor wherein the higher-pressure environment takes the form of atank at a higher level than the water supply air tank and in which theleakages from two pairs of deTection dip pipes of similar but unequallengths enter the higher-level tank, one pair of dip pipes indicatingthe top level and the other pair indicating the bottom level, and thepipes of these pairs communicating with pressure difference regulators.